Like I posted, the 7622 has full control on the unit itself. That is a nice feature. Mount it where you can reach it. The remote control switch makes it possible to visually see if the separator is open or closed. That's also a great feature.
Sure power also makes voltage sensing separators, but I had a lot of trouble with mine. Others have used them with good success. They are priced much cheaper.
Makes a great simple disconnect switch but it doesn't work automatically to tie the banks together when a charge is applied.
SMB doesn't install fusing on their builds or at least didn't on mine.
The fuse or breaker needs to be speced to the size wire, size battery bank and the load. I would install a 300A fuse if you plan to use 4/0 copper bus wire. The fuse has to be heavy enough to handle the load of a microwave, but using the house battery to jump start the vehicle could pull more than anything else. You don't want to blow a 150 amp fuse. The fuse is more there to prevent a fire during a direct short rather than protecting equipment.
I've never been able to find a 300A 12vDC breaker
For batteries there are several thoughts... none right or wrong.
Several small batteries can be easier to replace due to their size and weight, but more connections means more chances of trouble. Also one bad battery could kill the others when banked together.
A single 4-D or slightly larger 8-D might be all you need. With AGM batteries, they shouldn't drop below12.2 v by morning. I like to run my microwave at night w/o running the engine so I have two 4-D's. I prefer Lifeline or Concord (both are from the same Co) but Deka and Odyssey put out a good battery as well. There are others I don't know about. I'd stay away from Universal unless i got a real good deal.
A buddy of mine is looking at 6v AGM golf cart batteries.